1. Technical Field
The present invention relates in general to linking in a telecommunication system and in particular to a method for upgrading the link within the telecommunication system. Still more particularly, the present invention relates to a method and system for link establishment that accommodates different link protocols for providing backward compatibility within a telecommunication or information handling system.
2. Description of the Related Art
Today, most of the transmission between telephone exchanges is digital, but the transmission and the signaling between a local exchange and a customer is still analogue. Because different users have different requirements (telephony, fax, data) in the existing analogue network, it is necessary to use separate telephone lines with separate characteristics for the different users. To solve this problem a new universal interface has evolved. This new network evolution is called the Integrated Services Digital Network (ISDN). ISDN is a versatile network in which all kinds of information technology are transmitted in a digital format between terminals. The ISDN digital access provides the end users with the possibility of initializing end-to-end digital connections that can support a variety of services, such as: high quality speech, audio, video telephony, video conference, as well as fax, data and image transfer capabilities.
To ensure that voice and signaling or data and signaling information can be transmitted simultaneously in ISDN with no mutual reference, multiple channels are provided on an ISDN access and are defined by the International Telecommunication Union (ITU) in a series of protocol specifications. These channels are identified as B-channels and D-channels respectively. The B-channels are used for information transfer, such as speech, text, data and images. The D-channel is used for call control signaling procedures and may also be used to carry packet-switched data. The call control signaling information on the D-channel is used to establish, supervise and release the circuit-switched connections being requested for.
Unlike the B-channels, which function as xe2x80x9cpipes,xe2x80x9d the D-channel is associated with higher level ITU protocol specifications defined by an Open System Interconnection (OSI) model. The OSI model has 7 protocol specification layers in which layers 2 and 3 of the model form the packet-switched connections associated with the D-channel. Within the layer 3 protocol specifications for use on the D-channel is a call-control protocol component. This layer 3 signaling protocol is transferred on the D-channel using the layer 2 protocol referred to as the Link Access Procedure-D-channel (LAPD.) Although the layer 3 protocol takes care of most ISDN signaling requirements, the LAPD layer 2 protocol utilizes frames that play a very important role in terms of low-level signaling to ISDN devices. These LAPD frames contain the information to ensure that incoming calls are routed to the appropriate ISDN device, and pass the addressing information that distinguishes ISDN devices on a single line from each other.
To initially establish a point-to-point link between two terminals, a command frame is sent along the D-channel from a transmit terminal to a receive terminal. The command frame has a predetermined byte structure recognized at the receive terminal in accordance with the ITU protocol specification. However, a problem has arisen due to a new protocol introduced by the ITU that provides a different command frame for establishing a link that is not compatible with the old protocol specification. The problem arises when an upgraded terminal tries to establish a link with a terminal that does not recognize the different command frame and therefore has not been upgraded. Currently there is no method for determining which protocol terminals should be using when establishing a link.
Therefore, there is a need for a link establishment procedure in which the proper protocol between two terminals can be initially determined and invoked. The subject invention herein solves this problem in a new and unique manner that has not been part of the art previously.
It is therefore an object of the present invention to provide a method and system for upgrading a link within a telecommunication system or information handling system.
It is therefore another object of the present invention to provide a method and system for link establishment that accommodates different link protocols for providing backward compatibility within a telecommunication or information handling system.
The foregoing objects are achieved as is now described. A first link protocol utilizing a set mode command is sent from one or more transmit terminals to establish a link with one or more receive terminals. The set mode command comprises a frame format including an identifying byte field in accordance with International Telecommunication Union""s Q.921 Annex E protocol specification. The one or more transmit terminals wait a predetermined T200 time interval to receive a response from the one or more receive terminals to determine if the link is established. If a response is not received from the one or more receive terminals, the one or more transmit terminals resends the set mode command a predetermined N200 times. If the link is still not established within the predetermined N200 times, a second link protocol utilizing a set asynchronous balanced mode extended command having a different identifying byte field in accordance with International Telecommunication Union""s Q.921 protocol specification is sent to the one or more receive terminals to establish the link.
The above as well as additional objects, features, and advantages of the present invention will become apparent in the following detailed written description.